INTERNATIONAL ASSOCIATION OF PLUMBING
AND MECHANICAL OFFICIALS, UNIFORM EVALUATION SERVICES
EVALUATION CRITERIA FOR
TWISTED STEEL MICRO-REBAR (TSMR) IN CONCRETE
EC 015 – XXXX
(Adopted - November 2013, Proposed – October 2015)
1.0 INTRODUCTION
1.1
Purpose: The purpose of this evaluation criteria is to establish requirements for Twisted Steel
Micro Rebar (TSMR) in an independently reviewed evaluation report under the 2015, 2012 and
2009 International Building Code® (IBC) and the 2015, 2012 and 2009 International Residential
Code® (IRC). Bases of recognition are IBC Section 104.11 and IRC Section R104.11.
1.2
Scope: This evaluation criteria applies to Twisted Steel Micro Rebar (TSMR) used as an
alternative reinforcement to materials and methods specified for structural concrete designed and
constructed in accordance with ACI 318 and for structural slabs on grade designed and
constructed in accordance with ACI 360.
2.0 REFERENCED STANDARDS
2.1
General: Referenced standards shall be applied consistent with the provisions of the applicable
edition of the IBC and as noted herein.
American Concrete Institute
ACI 224.2-92
(2004)
Cracking of Concrete Members in Direct Tension
ACI 318-14
Building Code Requirements for Structural Concrete
ACI 318-11
Building Code Requirements for Structural Concrete
ACI 318-08
Building Code Requirements for Structural Concrete
ACI 360R-10
Guide to Design of Slabs-on-Ground
ASTM International
ASTM C39-14a Standard Test Method for Compressive Strength of Cylindrical Concrete
Specimens
ASTM C78-10e1 Standard Test Method for Flexural Strength of Concrete (Using Simple Beam
with Third-Point Loading)
ASTM C94-14
Standard Specification for Ready-Mixed Concrete
ASTM C192-07 Standard Practice for Making and Curing Concrete Test Specimens in the
Laboratory
ASTM C330-14 Standard Specification for Lightweight Aggregates for Structural Concrete
ASTM C494-13 Standard Specification for Chemical Admixtures for Concrete
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ASTM C1609-12 Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete
(Using Beam with Third-Point Loading)
ASTM E111-04
(2010)
Standard Test Method for Young's Modulus, Tangent Modulus, and Chord
Modulus
ASTM E119-2012A Standard Test Methods for Fire Tests of Building Construction and Materials
Canada Standards Association
CSA A23.2-16C Standard Test Method for Determination of Steel or Synthetic Fibre Content in
Plastic Concrete
International Code Council
2015, 2012 and 2009 IBC
2015, 2012 and 2009 IRC
AC208
International Building Code®
International Residential Code®
Acceptance Criteria for Steel Fibers in Concrete
International Organization for Standardization
ISO/IEC 17011:2004
ISO/IEC 17025:2005
Conformity Assessment--General Requirements for Accreditation Bodies
Accrediting Conformity Assessment Bodies
General Requirements for the Competence of Testing and Calibration
Laboratories
Japan Society of Civil Engineers
JSCE SF-4(1984)
Method of Test for Flexural Strength and Flexural Toughness of Steel
Fiber Reinforced Concrete, Japan Society of Civil Engineers
Underwriters Laboratories
UL 263-11
Standard for Fire Tests of Building Construction and Materials
3.0 DEFINITIONS
3.1
General. Where the following terms appear in this Evaluation Criteria, such terms shall have
the meaning as defined in this section.
Hybrid Design: A design that includes a combination of both deformed reinforcing bars and
TSMR.
TSMR Design Classes: There are four TSMR design classes. The registered design
professional shall select the appropriate design class based on the definitions below.
Class A – Temperature and Shrinkage Reinforcement: As a replacement for reinforcing bars
or welded wire reinforcement in any application as an alternative to minimum reinforcement for
the shrinkage and temperature reinforcement specified in Section 24.4 of ACI 318-14 (Section
7.12 of ACI 318-11 and -08) in members complying with the requirements of Section 14.1.3 (a or
b) of ACI 318-14 (Section 22.2.1 (a or b) of ACI 318-11 and -08). This application includes
replacement for temperature and shrinkage reinforcement in composite steel deck applications
specified in ANSI/SDI-C1.0 or ASCE 3 and other structural plain concrete structures designed
according to ACI 318-14 Chapter 14 (ACI 318-11 and -08 Chapter 22). The TSMR shall not be
used to replace any joints specified in ACI 318-14 Section 14.3.4 (ACI 318-11 and -08 Section
22.3).
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Class B - Minimum Structural Reinforcement. As a replacement for structural reinforcement in soilsupported structures including footings; structural concrete slabs supported directly on the ground
(designed in accordance with ACI 318 or ACI 360 Section 11.3.3, Elastic Method); foundations;
replacement for structural reinforcement in members in which arch action provides compression in the
cross-section; replacement of reinforcement in pile-supported slabs on ground with un-occupied space
below not to exceed the slab thickness (so failure will not result in structural collapse endangering
occupants) and designed in accordance with ACI 318; and as replacement for reinforcement in structural
walls in accordance with ACI 318 Chapter 14 and observing the following criteria:
•
•
•
Thickness of bearing walls shall be not less than 1/24 the unsupported height or length,
whichever is shorter, nor less than 5½ inches (140 mm).
Walls shall be braced against lateral translation (walls shall be laterally supported in such
a manner as to prohibit relative lateral displacement at top and bottom or on both sides of
individual wall elements, such as occurs with free-standing walls or walls in large
structures where significant roof diaphragm deflections).
Under the IBC, at least one No. 5 (16 mm) reinforcing bar shall be provided around all
window, door, and similar sized openings. Under the IRC, at least one No. 4 (12.7 mm)
reinforcing bar shall be provided around all window, door, and similar sized openings.
The reinforcing bars shall be anchored to develop fy in tension at the corners of openings.
Class C - Structural Concrete: As reinforcement for all other structural concrete including in
unsupported horizontal spans.
Class Cs – Non-Linear Slab Design: As reinforcement in structural slabs on ground designed in
accordance with ACI 360 Chapter 11.3.3 Methods 2 (Yield Line Analysis) and 4 (Nonlinear Finite
Element Analysis).
Twisted Steel Micro Rebar (TSMR): A steel rod or wire, with a non-circular cross section that
shall be twisted at least one time (360°) about its own axis. Used as discontinuous reinforcement,
the product is typically small enough to be mixed in large numbers into the concrete before
placement.
Twisted Steel Micro Rebar Design Crack Width, Sa: This is the crack width resulting from
tensile stresses typically measured for structural design applications. S a represents the average
upper limit of displacement in a direct tension test where the stress remains stable. S a is set forth
in Eq.-1:
Sa = δ + X/3
(Eq.-1)
Where:
δ = material elongation as stated on raw material certification test reports, inch (mm).
X = elongation from twist, representing the materials approximate ability to “stretch”
and need not be exactly determined, inch (mm).
(Eq.-2)i
Where:
n = number of full revolutions of the part
d = equivalent diameter of the wire, inches (mm)
L = length of the part, inches (mm)
X = percentage reduction in length from twisting the part
The resulting values of Sa are used as a reference point for computing tensile resistance and
compute maximum allowable crack width. In general the larger the Sa selected, the smaller the
tensile resistance and the larger the maximum allowable crack width. Sa shall not exceed 1.0
mm (0.04 inch).
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4.0 BASIC INFORMATION
4.1
General: The following requirements shall be considered in the evaluation of the TSMR:
4.2
Product Description: The following information on the TSMR as defined in Section 3.1 of this
criteria shall be submitted for inclusion in the evaluation report.
a. Raw Material Tensile Strength: The tensile strength for raw material shall be submitted
based on certification or mill tests supplied by the manufacturer.
b. Description of Shape: The cross sectional shape shall be described and shall be noncircular (has at least one flat edge).
c. Cross Sectional Area: The cross-sectional area shall be reported and computed from the
cross-sectional dimensions on the raw material certification or mill tests.
d. Minimum Twist: The TSMR twist shall be reported and there shall be at least one 360degree twist over the length of the product.
4.3
Fire Resistance: At least one roof and one floor concrete assembly designed to be reinforced
with TSMR shall be tested for fire resistance in accordance with ASTM E119 or UL 263. Fullscale fire resistance testing specific to the application is not required where an accompanying
engineering study prepared by a testing laboratory establishes the equivalency of the TSMR to
reinforcing bars in terms of fire resistance.
4.4
Installation Instructions: The manufacturer shall provide the evaluation service agency and the
laboratories conducting the testing a copy of its installation instructions. All test specimens, shall
be prepared in accordance with installation instructions and procedures used in the field.
4.5
Packaging and Identification: Method(s) of packaging and product identification shall be
included in the evaluation report. Identification shall include the manufacturer’s name and
address, product name, and the evaluation service agency’s evaluation report number.
4.6
Testing Laboratories: Testing laboratories shall be accredited for the applicable testing
procedures in accordance with ISO/IEC 17025 by a recognized accreditation body conforming to
ISO/IEC 17011. Testing at a non-accredited laboratory shall be permitted by the evaluation
service agency, provided the testing is conducted under the supervision of an accredited
laboratory and the supervising laboratory issues the test report.
4.7
Test Reports: Test reports shall comply with Annex A of this criteria.
4.8
Product Sampling: Sampling of the TSMR for tests under this criteria shall comply with Annex A
of this criteria.
5.0 TESTING AND PERFORMANCE REQUIREMENTS
5.1
TSMR Material - The testing laboratory shall examine TSMR specimens and verify information in
Section 4.2 of this criteria.
5.2
Basic Performance: The TSMR shall comply with AC208 at the minimum allowable dosage.
5.3 Tension Strength Specimens: Tension strength tests shall be conducted in accordance with
Section 6.1 of this criteria. As a minimum, the testing shall encompass the following:
5.3.1
5.3.2
TSMR: Each size of TSMR shall be tested.
Concrete Proportions: Each concrete mix design specified by the manufacturer,
characterized by compressive strength and aggregate size, shall be tested. For structural
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5.3.3
lightweight concrete, aggregate shall comply with ASTM C 330, size designation 1 inch
(25.0 mm) to 0.187 inch (4.75 mm).
Dosage Rates: For each concrete mix design, a range of TSMR dosage rates shall be
tested. The minimum and maximum dosage rates shall be tested along with at least one
intermediate dosage.
5.4
Data Analysis: The tensile test results shall be analyzed in accordance with Section 7.0 of this
criteria.
5.5
Performance Requirements: The tensile test results shall comply with requirements in Section
8.0 of this criteria.
5.6
Concrete Compressive Strength: Compressive strength specimens for each concrete mix
design containing the TSMR shall be cast, cured, and tested in accordance with applicable
sections of ASTM C192 and C39 respectively.
6.1
6.0 TEST METHODS
Direct Tensile Test: Testing shall be conducted at room temperature in accordance with ASTM
E111, with the following modifications:
6.1.1 Specimens shall be molded in a non-absorptive mold with the use of a form release
agent. The mold shall produce specimens similar to Figure 1 of this criteria.
6.1.2 The addition of TSMR shall comply with the published installation instructions.
6.1.3 Specimens shall remain in the molds for a period of 24 hours after casting and then cured
in accordance with ASTM C 192.
6.1.4 A universal joint shall be positioned at one end of the test specimen as shown in Figure 1
of this criteria.
6.1.5 Three displacement measuring devices with a resolution of 0.1 microns and an accuracy
of 1 micron shall be attached to the specimens to record actual displacement. The LVDTs
shall be centered about the middle of the gage length of the tension specimen. Figure 1
of this criteria illustrates the placement of the displacement devices.
6.1.6 A minimum of three replicate specimens for each configuration dosage and mix design
are required.
6.1.7 Anchoring: The specimen shall be anchored with a threaded rod capable of developing
the expected tensile force.
6.1.8 Test Machine: A universal tension tester capable of operating under the following
parameters is required:
6.1.8.1 Machine shall be capable of a sampling rate of 0.1 Hz minimum.
6.1.8.2 Machine shall be capable of 0.0005 in/min (0.0127 mm/min) co-axial movement
rate.
6.1.8.3 Machine shall be able to deflect at least 0.25 inches (6.4 mm)
6.1.8.4 Machine shall be capable of containing the coupon shown in Figure 1 of this
criteria.
6.1.9 Reporting: The reporting requirements listed in ASTM E111 Sections 10.1.8 and 10.1.9
shall be replaced with the following reporting requirements.
6.1.9.1 Tensile force vs. elongation curves shall be reported.
6.1.9.2 The peak tensile force shall be determined.
6.1.9.3 The tensile force and displacement immediately preceding the formation of the
first dominant crack shall be determined. The associated stress and strain
values shall be computed based on the section size and gage length.
6.1.9.4 The peak post-crack tensile strength shall be determined. This value is defined
as the peak load after 0.01 inch (0.25 mm) vertical displacement.
6.1.9.5 The tensile force at the strain limit (defined as Sa) shall be determined.
6.1.9.6 After the specimen is broken, the total number of TSMR on both faces of the
broken section extending out of the broken plane at least 0.040 inch (1.00 mm)
and at 30 degrees or greater (90 degrees defined as the TSMR being
perpendicular to the cracked plane) shall be summed.
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6.1.10 Concrete Compressive Strength Tests: Three cylinders shall be tested for each unique
mix design within 24 hours of tensile testing in accordance with Section 5.6 of this
criteria. The actual cylinder test results shall be reduced to the specified compressive
strength in accordance with ACI 318-14 Section 19.2.1 (ACI 318-11 and -08 Section
5.3.2.2).
7.0 TEST DATA ANALYSIS
7.1
From the tensile tests in Section 6.1 of this criteria, a general linear regression model shall be
developed, capable of predicting the tensile strength as a function of 1) the number of TSMR
present in the broken section as set forth in Section 6.1.9 of this criteria and 2) the specified
compressive strength of the concrete. The following requirements apply to the regression model:
7.1.1 The linear terms, the constant, and the standard deviation of each model shall be
reported.
7.1.2 However, enough tests shall be run to establish the number of TSMR linear term as a
statistically significant predictor (the maximum allowable p-value of this term is 0.05
indicating 95% significance).
7.1.3 Outliers and suspicious data points may be removed using standard statistical practices.
Outliers may not be removed from the test report and their removal from the regression
model shall be justified in writing along with the regression analysis results.
7.1.4 The overall average number of TSMR in the tests shall not exceed the midpoint of the
range of TSMR per unit area considered (the dosage may have a bias toward the upper
half of the range).
8.0
PERFORMANCE REQUIREMENTS
8.1
Strain Capacity Increase Requirement: Tensile test results shall indicate a statistically
significant increase (minimum of 95% confidence, the maximum p-value in a two sample t-test,
0.05) in tensile strain capacity compared to structural plain concrete. A minimum of six control
(plain concrete) specimens shall be considered in the analysis in addition to the minimum number
of TSMR samples required in Section 6.0. Since resolution of data can be an issue in
measurements of small deflections, data with slope coefficient of variation (COV) greater than 2
percent as computed according to ASTM E111, Section 9.2, Equation 4 may be neglected.
8.2
Post-Crack Tensile Stability Requirement: Tensile tests shall indicate that the median of the
load carried at Sa divided by the maximum load after 0.01 inch (0.25 mm) displacement is equal
to or greater than 0.85.
9.0
QUALITY ASSURANCE - FIELD INSPECTION:
9.1
The TSMR dosage (mass per unit volume applied to the mix) shall be certified in writing by
concrete supplier.
9.2
The tested concrete compressive strength shall be the greater of 3,000 psi (20 Mpa) for Class A,
Class B, and Class Cs, and 4,000 psi (27 Mpa) for Class C and specified compressive strength
for the design.
9.3
Compressive strength samples shall be cast, cured, and tested in accordance with applicable
sections of ASTM C192 and C39 respectively.
9.4
TMSR content (dosage) verification testing, when required, shall be conducted in accordance
with CSA A23.2-16C “Standard Test Method for Determination of Steel or Synthetic Fibre Content
in Plastic Concrete”. The average TSMR content (CSA A23.2-16C Section 9g) shall exceed
specified dosage minus the specified TSMR dosage x TSMR distribution coefficient of variation
(COV defined in Section 11.1.3.2 or 11.1.3.3 of this criteria). Annex B shows the step by step
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procedure for developing a table of limits for various TSMR dosages. TSMR content verification is
not required for the following TSMR applications:
9.4.1 Class A and B applications where one of three conditions exists which guarantee
stability: soil support, lateral support, or arch action as set forth in ACI 318-14 Section
14.1.3 (ACI 318-11 and -08 Section 22.2.1).
9.4.2 Applications designed with the minimum quantity of structural reinforcing bars in
accordance with ACI 318.
10.0
QUALITY ASSURANCE – MANUFACTURING:
10.1
Quality documentation complying with the IAPMO UES Minimum Requirements for Listee’s
Quality Assurance System (ES-010) or equivalent shall be submitted.
10.2
A qualifying inspection shall be conducted at each manufacturing facility by an approved
inspection agency. The approved inspection agency shall be accredited in accordance with
ISO/IEC 17020 by a recognized accreditation body conforming to ISO/IEC 17011.
10.3
An annual inspection shall be conducted at each manufacturing facility by an approved inspection
agency. The approved inspection agency shall be accredited in accordance with ISO/IEC 17020
by a recognized accreditation body conforming to ISO/IEC 17011.
11.0
11.1
APPLICATION
Analytical Model: Standard practices for computing bending moment and shear, or any other
resistance value based on the tensile strength of the concrete shall be used, replacing the tensile
contribution of the continuous reinforcement with the TSMR tensile force. The structural design
professional shall use the following procedure to design with TSMR.
11.1.1 Reinforcement Area: The nominal area of steel for the application shall be computed
using standard practice and ACI 318 assuming deformed continuous reinforcement is
used.
11.1.1.1 For Class A structural members, the structural design professional may
assume the reinforcing bars are in the center of the concrete section.
11.1.1.2 For Class B, C and Cs structural members, the structural design professional
shall determine the area of steel required at the depth of the centroid of the
tension region of the concrete section.
11.1.2 Area of Steel vs. TSMR Count Table (Figure 2 of this criteria): The evaluation report
shall include a table for each class of design consisting of at least two columns: 1) area of
reinforcing bars and 2) number of TSMR required to provide the yielding force equivalent
to the area of reinforcing bars listed in Column 1. The structural design professional shall
refer to this table to compute the number of TSMR required to provide the tensile
resistance equal to a given area of reinforcing bars. The force per TSMR shall be
determined using the regression model developed in Section 7.0 of this criteria. This
table may have additional columns for different concrete compressive strengths. The
manufacturer shall prepare the tables and the evaluation agency shall verify the
following:
11.1.2.1 Class A and B Structural Members: Micro-cracks occur and the TSMR remains
bonded to the concrete. The average embedded length is ½ the length of the
TSMR. The tensile test measures the response when the average embedded
length is only ¼ the length of the TSMR due to the formation of a dominant
crack. To obtain the maximum resistance, the tensile force at Sa shall be
multiplied by the ratio of the embedded lengths: L/2 divided by L/4 = 2 to obtain
the force per TSMR.
11.1.2.2 Class C and Cs Structural Members: A multiple crack condition occurs with
areas of localization. The average embedded length is L/4 due to the presence
of a full depth crack so no adjustment is needed and S a is used to derive the
force per TSMR.
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11.1.3 TSMR Count/Unit Area vs. Dosage Table (Figure 3 of this criteria): The evaluation
report shall include a table for each class of design, which includes at least two columns:
1) number of TSMR per unit area 2) TSMR dosage required to provide the number of
TSMR listed in column 1.
Additional columns may be provided to for different
compressive strengths of concrete. The structural design professional shall divide the
number of TSMR required by the area of concrete in tension and use this table to
determine the TSMR dosage that needs to be applied.
11.1.3.1 The percentage of TSMR active in resisting tension shall be 88.9 percent,
which is the percentage of all TSMR inclined 30 degrees or more relative to the
direction of the load.
11.1.3.2 The manufacturer may elect to conduct a series of tests as described in
Section 6.1 of this criteria to establish the COV at various dosages and present
the results to the evaluation agency.
11.1.3.3 In the absence of actual distribution data the manufacturer may elect to use
distribution data available in literature ii (Dupont, L. Vandewalle / Cement &
Concrete Composites 27 (2005) 391–398) In this case a copy of the data and
regression analysis used shall be provided to the evaluation agency.
11.1.4 TSMR Count / Unit Area vs. Tensile Stress Table (Figure 4 of this criteria): The
evaluation report may optionally include a third table, which relates the number of TSMR
per unit area to the corresponding tensile stress. Additional columns may be provided for
different concrete compressive strengths.
11.1.5 A resistance factor shall be applied the table values to address the variance in TSMR
performance in Class B and C structural members only. Average responses are used for
Class A and Cs structural members. The resistance factor shall be computed in
accordance with Eq-3 using standard LRFD statistical methods iii such that the tensile
strength provided by TSMR may be substituted into the design equations for continuous
reinforcement. A separate table shall be prepared for each design class.
(Eq-3)
Where:
is the target resistance factor
β is the beta factor defining the acceptable probability of failure (Section 11.2 of this
criteria).
Vr is combined coefficient of variation of the response model. The coefficient of
variation shall be computed using appropriate statistical laws as outlined by MacGregor
(MacGregor, J.G. Safety and limit states design for reinforced concrete, Can. J. Civ.
Eng. 3,284 (1976)).
11.2
Resistance Factor Calibration
The prediction of bending response from direct tension response can be overly conservative in
concrete because direct tension tests do not allow as much re-distribution of load as bending
tests allow. The manufacturer may optionally choose calibrate the Class B and C beta values
based on experience from laboratory and field-testing to correct for this offset. Calibration shall be
done by comparing bending moments predicted using the TSMR tensile stress quantities applied
as a rectangular stress block below the neutral axis to the peak and the average post-crack
bending moments of 3 or 4 point flexural tests on simple supports – e.g., ASTM C1609, ASTM
C78, JSCE SF-4, full scale bending tests, etc.).
11.2.1 The average post crack bending moment shall be computed as the average of the 1)
peak moment, 2) the moment at the midpoint deflection corresponding to a single crack
width equal to Sa and 3) the moment at half of this midpoint displacement). The overall
average factor of safety versus the 1) peak and 2) average post crack strength shall be
determined. The mid-point deflection may be determined using the following similar
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triangles approach. Crack width at mid-span shall be estimated in accordance with Eq-4.
(Eq-4)
Where
h is the height of the beam, inches (mm)
δ is the mid-span deflection, inches (mm)
span is the unsupported distance between supports, inches (mm)
Class A and Class Cs designs are based on average values so β shall be set
to zero for these design classes. No calibration is required for these classes.
11.2.2 Class B design is based on micro-cracking behavior so a minimum average factor of
safety vs. peak post crack strength of 4 shall be observed with less than 1:20 overpredictions (based on β of 1.5 at peak). The β may be adjusted until this requirement is
achieved.
11.2.3 Class C design is assumes localized cracking behavior so the minimum average factor of
safety vs. average post crack strength of 2 shall be observed with less than 1:20 overpredictions (based on β exceeding 1.5 at average post crack). The β may be adjusted
until this requirement is achieved.
11.2.4 A third party testing laboratory, or customer shall perform tests used for calibration
purposes. Since the purpose of calibration is to adjust the model to estimate
performance under localized conditions and actual users conduct many of these tests,
testing need not be conducted at accredited facilities. The testing laboratory may be
exempt from accreditation where test results are provided and a registered design
professional who reviews the data and calibration computations and agrees with the
submitted results.
11.3
Performance Based Alternative: The design criteria outlined in this section as well as the
limitations in Section 12.0 of this criteria may be modified or waived if the registered design
professional shows through analysis or testing conformance to the performance requirements of
the application, as also allowed in ACI 318-14 Section 1.10 (ACI 318-11 and -08 Section 1.4),
IRC and IBC Section 104.11, and relevant ACI code cases iv.
12.0
LIMITATIONS
12.1
Class Application Limits: The permitted applications for each class are described in detail in
Section 3.1 of this criteria.
12.2
Class A and B Strain Limits: The average tensile strain in the concrete shall not exceed the
average increase in tensile strain determined through direct tension testing set forth in Section
6.1 of this criteria. The average tensile strain in may be estimated by dividing the tensile stress in
the concrete by the modulus of elasticity of the concrete (Hooke’s Law). If the limit is not satisfied,
Class C design is required. For Class A and B Table 3 (Figure 4 of this criteria) shall be utilized to
select the provided TSMR unit tensile strength. The average strain shall be calculated in
accordance with Eq-5:
(Eq-5)
Where:
Ect is the tensile modulus of elasticity of concrete containing TSMR, estimated as 57,000
or 4200
(MPa).
ε is the average concrete tensile strain
(psi)
Note: this calculation is not meant to be a predictor of crack formation but rather a predictor of the
concrete’s ability redistribute loads by having at least enough tensile strain capacity at the
centroid of the tensile region to resist formation of a full depth dominant cracks. These types of
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cracks eliminate alternative load paths and the ability for the loads to re-distribute through-out the
member.
The baseline tensile strain capacity shall be set at 70 micro-strain (0.00007). This value is based
on equations for the direct tensile strength (first crack strength) of normal-weight concrete set
forth in ACI 224.2R Equation 3.2 and Ec shall be computed from ACI 318-14 Section 19.2.2.1
(ACI 318-11 and -08 Section 8.5.1). The TSMR strain limit shall be set at one plus the percent
increase determined in accordance with Section 8.1 times this baseline. While the equations
provide some differences for lightweight concrete, the change is not significant enough to require
re-computation of the baseline strain. The strain increases with TSMR dosage. A simple
regression analysis shall be performed to establish three or more strain limits based on average
increase in strain within each range versus TSMR content per unit area. The strain increase shall
not exceed the 90th percentile of all data collected for the strain increase derivation in Section 8.1
of this criteria.
In cases of prestressed concrete, the initial compressive strain may be subtracted from strain
calculated according to Eq-5. In cases of restrained shrinkage and joint-less slabs, the estimated
shrinkage strain shall be added to the strain computed from Eq-5. Several methods of strain
computation are available. The structural design professional shall select an appropriate method
to calculate these tensile strain values. TSMR shall not be used to replace post-tension and prestressing strands except as provided in Section 11.3 of this criteria. The addition of TSMR does
not change the prestressed design procedure.
12.3
Class C Structure Limitations
12.3.1 Bar reinforcement is not required in any structural member where strains exceeds the
Class A or B strain limits but conforms to the Class A or B application limitations listed in
Section 3.1 of this criteria. The structural design professional, may, however elect to use
a combination of bar reinforcement and TSMR for these applications.
12.3.2 Bar reinforcement is required in any structure not complying with the Class A and B
application limitations listed in Section 3.1 of this criteria. The minimum quantity shall be
as prescribed in ACI 318-14 Section 9.6.1.2 (ACI 318-11 and -08 Section 10.5.1) or other
code-required minimum structural reinforcement for the application.
12.3.3 Unsupported horizontal spans (free-spanning beams or slabs with occupied space above
or beneath) shall have the minimum amount of bar reinforcement required by ACI 318 to
resist nominal service loads.
12.3.4 Strength provided by non-composite stay-in-place forms for installations not complying
with the Class A and B application limitations may be used to satisfy the minimum
reinforcement requirement provided the structural design professional designs the forms
to provide resistance equal to or greater the resistance than provided by the required bar
reinforcement. The TSMR dosage shall be adequate to support the entire load and the
contribution of the stay-in-place forms shall not be added to the TSMR capacity.
12.3.5 The requirement for reinforcing bars may be waived based on acceptable data in
accordance with Section 11.3 of this criteria.
12.4
Class A and B Hybrid Design
12.4.1 Hybrid design is allowed for Class A and B structural members with no minimum
reinforcing bar requirement when the application limits listed in Section 3.1 of this criteria
and strain limits in Section 12.2 of this criteria are satisfied.
12.4.2 If Class A or B application limits listed in Section 3.1 of this criteria are satisfied but the
strain limit in Section 12.2 of this criteria is exceeded, the structural member may be
designed as Class B Hybrid. This process will reduce the strain computed in Section 12.2
of this criteria. The strain limit may be waived if the minimum amount of bar reinforcement
as prescribed in ACI 318-14 Section 9.6.1.2 (ACI 318-11 and -08 Section 10.5.1) is
provided. Alternatively, the structural design professional may elect to design the
structural member as Class C without the need for bar reinforcement.
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12.5
Dosage and Compressive Strength Limitations: Minimum and maximum dosages and
concrete compressive strengths shall be set at levels consistent with the upper and lower bounds
of the tensile testing program. Extrapolation above and below the tested concrete compressive
strengths and TSMR counts is not permitted.
12.6
Flexure Limitations: For flexure, standard balanced and tension-controlled strain limits as
prescribed in ACI 318-14 Section 21.2.2 (ACI 318-11 and -08 Section 10.3) shall apply.
12.7
Shear Restrictions:
12.7.1 Use of TSMR for replacing shear reinforcement in Class A and Cs structural members is
not allowed.
12.7.2 The contribution of plain concrete shall be neglected in applications like shear (do not
add Vc to the shear resistance computed for TSMR). The direct tension tests used to
characterize the material include the effect of the concrete.
12.7.3 The area in tension shall be taken as the 1.41 x the section width x height minus 4 inches
(100 mm). This represents the 45-degree plane between the two layers of original
reinforcement.
12.8
Approval: A registered design professional shall approve use of TSMR.
12.9
Precast Concrete: TSMR shall not be used to replace supplemental reinforcing bars placed
around openings and tied to lifting points. Precast concrete may be designed as Class B even if
the class B application limitations are exceeded based on acceptable data in accordance with
Section 11.3 of this criteria.
12.10
Concrete Mixtures: When TSMR is added at the ready-mix plant, a batch ticket signed by a
ready-mix representative shall be available to the code official upon request. The delivery ticket
shall include, in addition to the items noted in ASTM C94, the type and amount of TSMR added to
the concrete mix.
13.0 Evaluation Report Recognition
13.1
General: The Evaluation Report shall include the following:
13.2
Basic information required by Section 4.0 of this criteria including product description, packaging
and identification.
13.3
Description of TSMR design classes and application limits in accordance with Section 3.1 of this
criteria.
13.4
Design instructions and tables in accordance with Section 11.0 of this criteria.
13.5
Limitations in accordance with Section 12.0 of this criteria.
13.6
Use of TSMR for Class C structural members in structures assigned to Seismic Design
Categories C, D, E, and F is outside the scope of this report.
13.7
For design of Class Cs structural members, applicable design provisions from ACI 360.
13.8
Description of qualified fire-resistance-rated assemblies in accordance with Section 4.2 of this
criteria.
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Figure 1 -- Tension Specimen Molds
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Table 1: TMSR replacement - Imperial
Nominal number of TMSR required
Fy = 60 ksi
Nominal area
of steel in
tension
As (in²/ft)
3000 psi
Class A & B
4000 psi
Class C & Cs
Class A & B
Class C & Cs
Figure 2 – Table 1
5000 psi
Class A & B
Class C & Cs
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Table 2: TMSR dosage rate - Imperial
Number of
TMSR per
unit area in
tension
(TMSR/in2)
TMSR dosage rate, Hd (lb/yd 3)
3000 psi
4000 psi
5000 psi
Class A Class B Class C Class Cs Class A Class B Class C Class Cs Class A Class B Class C Class Cs
Figure 3 – Table 2
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Table 3: TMSR tensile force - Imperial
Number of
TMSR per
unit area in
tension
(TMSR/in2)
Provided TMSR unit tensile stress, ɸFht (psi )
3000 psi
4000 psi
5000 psi
Class A Class B Class C Class Cs Class A Class B Class C Class Cs Class A Class B Class C Class Cs
Figure 4 – Table 3
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Annex A
Test Report Content
1.0
2.0
3.0
The services performed by the testing laboratory shall be documented by a retrievable
report that accurately, clearly, objectively, and unambiguously presents measurements,
observations, examinations, and test results in accordance with the reporting
requirements of test method(s). Each test or inspection report also shall include the
following unless the code, evaluation criteria, or the test standard requirements specify
otherwise:
1.1
A title, for example, “Report of TSMR Tests;”
1.2
The name, address, and contact information of the laboratory.
1.3
A unique identification of the report (such as report number), the issue date, a
sequential number for each page, and the total number of pages.
1.4
The name and address of client.
1.5
Description of, condition of, and clear identification of the item tested.
1.6
Date test(s) were conducted.
1.7
Identification of test standards or description of any non-standard methods used.
1.8
Any deviations from, additions to, or exclusions from, the test standard and any
other information relevant to the specific test, such as environmental conditions;
1.9
Measurements, observations, examinations, and test results, supported by
tables, graphs, sketches, and photographs, as appropriate, including a
description of the failure mode or condition of item at conclusion of the tests;
1.10
Conclusions or summary statements, including, when applicable, a statement
indicating whether the product passed or failed the test;
1.11
A statement the results apply only to the items tested;
1.12
A statement that the report shall not be reproduced, except in full, without the
prior written approval of the laboratory; and
1.13
Name(s) of individual(s) performing the tests;
1.14
A signature and title, or an equivalent identification, of the person(s) accepting
responsibility for the content of the report on behalf of the laboratory.
1.15
Identification of results obtained from tests subcontracted by the laboratory to
others. The laboratory shall not represent the services of others as its own.
In addition to the requirements of Sections 1.0, 2,0 and 3.0, each test report, where
necessary for the proper interpretation or understanding of the report, shall include the
following:
2.1
Project title and reference designation.
2.2
Reference to relevant code, evaluation criteria, or other requirement(s).
2.3
A statement indicating compliance with relevant code, evaluation criteria, or other
requirement(s).
2.4
Other reporting requirements of the evaluation agency, the client, or relevant
authority.
In addition to the requirements of Sections 1.0, 2.0, 3.0 and 4.0, test reports presenting
results shall include the following with respect to sampling:
3.1
Date of sampling or date sample received, as appropriate.
3.2
Clear identification of the material sampled including manufacturer, brand name,
lot number, source, or similar unique information, as applicable.
3.3
Sampling location, where relevant, using an explicit description, diagram, sketch,
or photograph, as applicable.
3.4
Identification of sampling methods used, or sampling plan or procedure if a nonstandard method was used.
3.5
Deviations from, additions to, or exclusions from standard sampling methods or
predetermined sampling plans or procedures.
3.6
Details of environmental conditions present during the sampling such as rain or
freezing weather that may have affected the testing of the sample or the
interpretation of the test results.
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3.7
4.0
5.0
6.0
If assemblies are tested (structural assemblies, fire-rated assemblies, etc.),
identification of the assemblies, preferably with illustrations. The report shall
identify the parties constructing the assemblies and shall also address witnessing
and/or verifying the construction.
When interpretations of tests are included in the report, the basis for the interpretations
shall be clearly explained. Interpretations commonly include determination of compliance
or noncompliance of the results with requirements of the test method or evaluation
criteria.
Material revisions or additions to a report after initial issue shall be made in a further
document clearly indicating the revised information and clearly referencing the original
report identification. Such revisions or additions shall meet the relevant requirements of
Section 2.0.
Transmission of test reports by electronic means shall follow documented procedures to
ensure that the requirements of this evaluation criteria are met and that confidentiality is
preserved.
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ANNEX B
Method for Calculating the Acceptable Limits for a TSMR Dosage
Using the provisions determined in Section 11.1.3 of this criteria, the coefficient of variation, COV, for the
distribution of TSMR micro rebar is
(1)
Using Equation B1, the acceptable coefficient of variation can be calculated for any given TSMR dosage
in lb/yd3. Equation 1 can only be used with dosages expressed in lb/yd 3, if a dosage is required for metric
units, the desired dosage shall be converted to lb/yd3 and then used with Equation B1.
To determine the limits, definition of the coefficient of variation shall be computed by Equation B2:
(2)
Where σ is the standard deviation and μ is the mean. To determine the acceptable TSMR dosage limit,
the mean for the TSMR dosage shall be taken as equivalent to the intended TSMR dosage of the
concrete mix. For the calculation of an acceptable TSMR dosage limit, one standard deviation shall be
taken as the acceptable deviation from the intended TSMR dosage.
By rearranging Equation B2, the acceptable deviation for a given TSMR dosage becomes Equation B3:
(3)
The lower acceptable dosage limit, LADL, , is then calculated using the Equation B4:
(4)
The LADL can then be used as an established acceptable lower bound for an intended TSMR dosage
when paired with the TSMR Wash out test. This lower bound ensures that an adequate distribution of the
TSMR fibers within the concrete mix is achieved.
A table can be developed to using these calculations showing the oz/cubic foot (grams/Liter) required and
included in the ESR for common TSMR dosages. Samples are included (Table B1 and B2).
Specified
TSMR Dosage
(lb/yd3)
Coefficient
of Variation
Standard
Deviation
(lb/yd3)
Lower Dosage
Test Limit
(oz/ft3)
5
0.271
2.12
2.16
10
0.212
2.50
4.67
…
…
…
…
60
0.019
34.89
2.12
Table B1. Example Acceptable limits for intended TSMR dosages of a 9 cubic yard truck, English Units
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Specified
TSMR Dosage
(kg/m^3)
Coefficient
of Variation
Standard
Deviation
(kg/m^3)
Lower Dosage
Test Limit
(g/L)
2.92
0.299
0.87
2.05
5.84
0.260
1.52
4.33
…
…
…
35.06
0.063
…
2.20
32.86
Table B2. Acceptable limits for intended TSMR dosages of a 7 cubic meter truck, SI Units
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APPENDIX A
(NONMANDATORY INFORMATION)
1. General
It is recommended that any evaluation report developed in accordance with EC 015 contain
instructions and figures similar to what in included herein along with several worked out example
problems to assist the designer.
2. Design in accordance with ACI 318 (Structural Concrete)
Designs governed by ACI 318-14 Section 1.10 (ACI 318-11 and -08 are in compliance with Section
1.4) (Approval of special systems of design or construction). For more details, see EC 015 Section
1.0 and ACI Public Discussion, Code Case ACI 318-08/001(12) and 318-11/001(12), Concrete
International, V. 35, No. 2, Feb. 2013, p. 67)v. Design instructions are provided in Sections 4.1 to 4.4
of this Appendix.
3. Design in accordance with ACI 360 (Slabs on Grade)
Slab on grade design is outside the scope of ACI 318 and alternatively may be done is done in
accordance with ACI 360. Design instructions are provided in Section 4.5 of this Appendix.
4. Design Instructions
4.1. Flexural Design Follow steps below to compute TMSR dosage using the tables developed in
accordance with EC015.
4.1.1.Determine Design Class using the definitions in EC015 Section 3.1
A flow chart (Figure 5) simplifies the class selection processv.
4.1.2.Compute Required Area of Steel
Determine the required area of steel at the centroid of the tension zone (TSMR acts as a
rectangular tensile block as shown in Figure 6) with standard design procedures
recommended in ACI 318-14 Chapter 6 (ACI 318-11 and -08 Chapter 8) using load and
resistance factor design. Use the calculated nominal area of steel in the procedure
described in Section 4.1.3 of this Appendix. An appropriate strength reduction factor will be
applied to the TMSR design strength.
4.1.3.Table 1: Required TMSR
Use Table 1 to select the minimum number of TMSR required to provide the same tensile
resistance as the area of steel computed in Appendix A Section 4.1.2. Divide this number
by the area of the concrete in tension to obtain the number of TMSR required per unit area.
This can be either direct tension, flexural tension, or shear.
4.1.4.Table 2: TMSR Dosage
Use Table 2 to select the minimum TMSR dosage required to ensure the number of TMSR per
unit area (as determined in Appendix A Section 4.1.3) are provided in the tensile region of the
concrete. The TMSR dosage listed in the table is calibrated using LRFD methods.
4.1.5.Table 3: TMSR tensile force
Use Table 3 to select the provided TMSR unit tensile strength. This value can be multiplied
by the effective area in tension to compute the total tensile resistance.
4.1.6.Compute strain in the composite
For Class A and B use Table 3 to select the provided TMSR unit tensile strength and
calculate the average strain with Equation A1:
Equation A1
Where:
ε ≅𝐓𝐌𝐒𝐑tensile stress/ECT
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 Ect is the tensile modulus of elasticity of TMSR concrete estimated as 57000
4200
(MPa).
 ε the average concrete tensile strain
(psi) or
4.1.7. Pre- or post-tensioned concrete
With pre- or post- tensioned concrete, the initial compressive strain may be subtracted
from the average strain calculated in Equation A1.
4.1.8. Restrained shrinkage
In cases of restrained shrinkage, the shrinkage strain shall be added to the average
strain computed in Equation A1.
4.2. Shear: The same method as above is used for shear and torsion reinforcement. The Area in
tension should be taken as no more than the 1.41 x the section width x height minus twice the
neutral axis depth. When replacing both bending and shear reinforcement the higher of the two
dosages governs the design.
4.3. Class A And B Strain Limits: The average tensile strain (Appendix A Section 4.1.6-4.17 and
4.18) in the concrete shall not exceed limits established in EC 015 Section 12.2.
4.4. Hybrid Design
A combination of standard reinforcement and TMSR may be used. For Hybrid Design, reduce
the area of steel computed in Section 4.1 of this criteria by the cross sectional area of the rebar
that will remain prior to determining the required minimum number of TMSR using Table 1.
4.5. ACI 360 Design Instructions
4.5.1.Class A and B Design in accordance with ACI 360-10 Section 11.3.3.2 (Elastic Design
Method).
Substitute
where
is used in ACI 360-10 Section 11.3.3.2
equations. All other calculations remain the same.
4.5.2.Class Cs Design with Yield Line Methods ACI 360-10 Section 11.3.3.3, Substitute
where
is used in ACI Section 11.3.3.3 equations. All other calculations
remain the same.
4.6. Limitations/Restrictions
All designs are subject to the limitations outlined in Section 12.0 of this criteria.
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Figure 5: TSMR Class Selection Flow Chart
b
εu
a
ᵃ/₂
C
c
dH
h
h-c
Tension face
εc
Strain
FH
Equivalent rectangular
stress block
Figure 6: TMSR Flexural Stress Block
i
Lagoudas, Dimitris L., and Walter E. Haisler, "Introduction to Conservation Principles and Applications in
Continuum Mechanics," Summer 2002, 450 pages. <http://aeweb.tamu.edu/haisler/engr214/Word
_Lecture_Notes_by_Chapter/chapter12- part1.doc>
ii
Dupont, D and Vandewalle, L, (2005) Distribution of steel fibres in rectangular sections. Cement and Concrete
Composites 27(3):391-398.
iii
MacGregor, J.G., “Safety and Limit States Design for Reinforced Concrete,” Canadian Journal of Civil
Engineering, V. 3, No. 4, Dec. 1976, pp. 484-513.
iv
Public Discussion, Code Case ACI 318-08/001(12) and 318-11/001(12), Concrete International, V. 35, No. 2, Feb.
2013, p. 67.
v Pinkerton, L and Novak, J & Stecher, J “Twisted Steel Micro-Reinforcement”, Concrete International, October
2013, pp 57-61).